1. Field of the Invention
The present invention relates to a rotary pump for sucking and discharging fluid and a braking apparatus using the rotary pump. In particular, the present invention is preferably applied to an internal gear pump such as a trochoid pump or the like.
2. Description of Related Art
There is a trochoid pump as one type of an internal gear rotary pump. FIG. 22 shows such a trochoid pump. As shown by the drawing, the trochoid pump is constituted by an inner rotor 701 having an outer teeth portion 701a at its outer periphery, an outer rotor 702 having an inner teeth portion 702a at its inner periphery, a casing 704 for containing the outer rotor 702 and the inner rotor 701. The inner rotor 701 and the outer rotor 702 are arranged in the casing 704 in a state where the inner teeth portion 702a and the outer teeth portion 701a are in mesh with each other and a plurality of gap portions 703 are formed by the respective teeth.
When a line running on respective central axes Xxe2x80x2 and Yxe2x80x2 of the outer rotor 702 and the inner rotor 701 is defined as the center line Zxe2x80x2 of the pump, an intake port 705 and a discharge port 706 respectively communicating with the plurality of gap portions 703 are formed on both sides of the center line Zxe2x80x2. When the pump is driven, the inner rotor 701 rotates with the central axis Yxe2x80x2 as a drive axis. In accordance therewith, the outer rotor 702 also rotates in the same direction by mesh between the outer teeth portion 701a and the inner teeth portion 702a. In this case, each of the gap portions 703 changes from a large volume to a small volume and vice versa during a time period in which the outer rotor 702 and the inner rotor 701 make one turn. Due to that volume change, oil is sucked from the intake port 705 and discharged to the discharge port 706.
In the internal gear pump such as a trochoid pump operating in this way, oil may leak from a clearance between the outer rotor 702 and the inner rotor 701. The oil leakage is caused since the outer rotor 702 is separated from the inner rotor 701 and a clearance is produced at a gap portion of which the volume becomes its maximum among the plurality of gap portions 703 owing to a pressure difference between discharge pressure and intake pressure.
The gap portion of which the volume becomes its maximum, is a closed gap portion which communicates neither with the intake port 705 nor the discharge port 706. Therefore, it maintains the pressure difference between the discharge pressure and the intake pressure and plays an important role in the pump smoothly carrying out intake and discharge operations. Accordingly, when the oil leakage as mentioned above happens, smooth pump operation cannot be carried out. For example, there arise problems such that a rotating unit is locked and high pressure oil cannot be discharged.
Hence, according to, for example, Japanese Unexamined Utility Model Publication No. JP-U-5-6170, oil leakage is prevented by reducing the clearance between the outer rotor 702 and the inner rotor 701.
Specifically, a clearance L1 between the outer rotor 702 and the casing 704 at a vicinity of the position where the volume of the gap portion becomes its maximum, is made smaller than a clearance L2 between the outer rotor 702 and the casing 704 at a vicinity of the closed gap portion (having minimum volume) opposed to the closed gap portion having the maximum volume. As a result, the clearance between the outer rotor 702 and the inner rotor 701 at the closed gap portion having the maximum volume is prevented from widening. However, in this case, because of high pressure fluid leaking from the discharge port 706 to the outer periphery of the outer rotor 702, the outer rotor 702 is pushed to a portion of the inner face of the casing 704 (point P) on the right side of the drawing.
Generally, the outer rotor 702 and the inner rotor 701 have fabrication errors in fabrication steps. Therefore, heights (length in diameter direction) of the teeth of the inner teeth portion 702a and heights (length in diameter direction) of the teeth of the outer teeth portion 701a are different from each other, respectively. Therefore, in setting clearances among a drive shaft, the inner rotor 701, the outer rotor 702 and the casing 704, the clearances are set by, for example, a method in which a maximum height tooth of the inner teeth portion 702a engages with a maximum height tooth of the outer teeth portion 701a. 
However, as mentioned above, heights of the teeth of the inner teeth portion 702a and the heights of the teeth of the outer teeth portion 701a are different from each other, respectively. Accordingly, when the closed gap portion having the maximum volume is formed by a tooth of the inner teeth portion 702a and a tooth of the outer teeth portion 701a which are shorter than the respective maximum height teeth thereof, a clearance is produced between the inner teeth portion 702a and the outer teeth portion 701a at the closed gap portion and oil leaks from the clearance.
Further, when the discharge pressure becomes high, force pushing the outer rotor 702 to the portion of the inner face of the casing 704 (vicinity of point P) on the right side of the drawing becomes large. Therefore, the pump may not be driven smoothly or the driving of the pump may be impossible since the outer rotor 702 are locked by being squeezed by the the casing 704 and the inner rotor 701.
The present invention has been made in view of the above-described problems and it is a first object of the present invention to provide a rotary pump capable of carrying out high pressure discharge by preventing fluid leakage and capable of being driven stably even when discharge pressure is high. Further, it is a second object of the present invention to provide a braking apparatus carrying out braking operation by using the rotary pump.
In a rotary pump according to a first aspect of the present invention, the outer rotor and the inner rotor are assembled in a casing such that, when a clearance between an inner teeth portion of an outer rotor and an outer teeth portion of an inner rotor is substantially nullified on a side of a first closed portion, which is a gap portion having a maximum volume, a clearance between the outer rotor and the casing on the outer periphery of the outer rotor on a side where the first closed portion is formed and a clearance between the outer rotor and the casing on a side where a second closed portion, which is the gap portion having a minimum volume is formed, become substantially an equivalent interval.
By such a constitution, an outer periphery of the outer rotor and an inner peripheral wall of the casing can be brought into contact with each other on the side of the second closed portion in view from the central axis of the inner rotor. Accordingly, even in a high pressure discharge operation, the outer rotor is not locked by being squeezed between the inner rotor and the casing and accordingly, the pump can be driven stably. Further, by torque transmitted from the inner rotor, the outer rotor is moved in a direction of contracting the clearance at the first closed portion. Accordingly, oil leakage between the outer teeth portion and the inner teeth portion at the first closed portion can be prevented.
Further, assembling operation may be carried out such that a clearance between the inner rotor and a drive shaft on the side where the first closed portion is formed may be set to be a half of the clearance between the inner rotor and the drive shaft.
The inner rotor and the outer rotor may be assembled in the casing such that a highest tooth portion of the inner teeth portion and a highest tooth portion of the outer teeth portion are disposed on a line defined by connecting the central axis of the outer rotor and the central axis of the inner rotor and on the side where the first closed portion is formed.
When the outer rotor and the inner rotor are rotated, teeth having the heights lower than the highest tooth portions of the inner teeth portion and the outer teeth portion, necessarily come on the line defined by connecting the central axis of the outer rotor and the central axis of the inner rotor and on the side where the first closed portion is formed. Accordingly, the outer periphery of the outer rotor and the inner peripheral wall of the casing can be brought into contact with each other on the side of the second closed portion in view from the central axis of the outer rotor. As a result, the pump can be driven stably without locking the outer rotor by being squeezed between the inner rotor and the casing even in the high pressure discharge operation.
Further, it is preferable to provide a low pressure side communicating path communicating the intake port and the outer periphery of the outer rotor on the side of the intake port and a high pressure side communicating path communicating the discharge port and the outer periphery of the outer rotor on the side of the delivery port. Thereby, pressures on the outer periphery and the inner periphery (teeth face side) of the outer rotor on the side of the discharge port as well as on the side of the intake port can be balanced. Accordingly, force of bringing the outer rotor in contact with the casing by oil pressure can be reduced and sliding resistance of the outer rotor can be reduced. That is, stable and excellent pump operation can be achieved with no locking and with small reduction in the rotational number of a drive motor.
It is also preferable to install first and second seal members for restraining flow of fluid in respective intermediaries between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor.
In this way, by providing the first and the second seal members for sealing the high pressure portion from the low pressure portion on the outer periphery of the outer rotor, leakage of fluid from the high pressure portion to the low pressure portion can be prevented. Thereby, the volumetric efficiency of the pump can be promoted and at the same time, the above-described effect can further be promoted. That is, by preventing leakage, pressures on the outer periphery and the inner periphery (teeth face side) of the outer rotor can be balanced further excellently.
Further, when the above-described rotary pump is applied to a braking apparatus, the rotary pump may be disposed in an auxiliary conduit while the intake port thereof is connected to the side of a brake fluid pressure generating device and the discharge port thereof is connected to the side of a braking force generating device. Further, instead of connecting the intake port to the brake fluid pressure generating device, for example, a master cylinder, it may be connected directly to a reservoir of the master cylinder.
In the braking apparatus having such a constitution, the brake fluid pressure within the auxiliary conduit becomes high when a braking operation is carried out by a driver. However, as mentioned above, even in the high pressure discharging operation, stable pumping operation can be carried out without causing oil leakage at the first closed portion and without the outer rotor locked by being squeezed between the inner rotor and the casing. Thereby, there can be provided a braking apparatus capable of excellently carrying out braking operation by using the above-described rotary pump.
In a rotary pump according to a second aspect of the present invention, a low pressure side communicating path for communicating an outer periphery of an outer rotor on a side of an intake port with a portion having a pressure equivalent to a pressure of the intake port and a high pressure side communicating path for communicating the outer periphery of the outer rotor on a side of a discharge port with the discharge port are formed in a casing. In particular, the low pressure side and high pressure side communicating paths are formed at positions for moving the outer rotor in a direction of pushing an outer teeth portion of an inner rotor forming a closed gap portion by an inner teeth portion of the outer rotor forming the closed gap portion.
When the outer rotor is moved in the direction of pushing the outer teeth portion of the inner rotor forming the closed gap portion by the inner teeth portion of the outer rotor forming the closed gap portion, a clearance between the inner teeth portion and the outer teeth portion are not widened by a difference between a pressure at the intake port and a pressure at the discharge port. Accordingly, when the positions of forming the low pressure side and high pressure side communicating paths are set for moving the outer rotor in the direction for pushing the outer teeth portion of the inner rotor forming the closed gap portion by the inner teeth portion of the outer rotor forming the closed gap portion, a clearance between the outer rotor and the inner rotor can be eliminated and leakage of fluid from the clearance can be prevented.
Further, the outer periphery of the outer rotor and the intake port can be communicated with each other by the low pressure side communicating path by selecting the intake port per se as a portion having pressure equivalent to pressure of the intake port.
Further, a specific position of forming the low pressure side communicating path is as follows. That is, in the case where the intake port is communicated with a plurality of gap portions, when the low pressure side communicating path is constituted by a first communicating path and a second communicating path, the first communicating path may be formed at a position where a gap portion adjacent to the closed gap potion among the plurality of gap portions communicating with the intake port, communicates with the outer periphery of the outer rotor and the second communicating path may be formed at a position where a gap portion distant from the closed gap potion among the plurality of gap portions communicating with the intake port, communicates with the outer periphery of the outer rotor.
Meanwhile, as a specific position of the high pressure side communicating path, in the case where the discharge port is communicated with a plurality of gap portions, the high pressure side communicating path may be formed at a position where a gap portion adjacent to the closed gap portion among the plurality of gap portions communicating with the discharge port, communicates with the outer periphery of the outer rotor.
When the above-described rotary pump is applied to a braking apparatus, in a braking apparatus having a main conduit for transmitting a brake fluid pressure from a brake fluid pressure generating device to a braking force generating device and an auxiliary conduit provided between the brake fluid pressure generating device and the braking force generating device in parallel to the main conduit, the rotary pump is installed at the auxiliary conduit so that an intake port thereof is directed to a side of the brake fluid pressure generating device and a discharge port thereof is directed to a side of the braking force generating device.
According to that braking apparatus, pressure of the braking fluid within the auxiliary conduit becomes high when a braking operation is carried out and the brake fluid pressure generating device generates the brake fluid of high pressure. At this time, a difference between pressure applied on the intake port and pressure applied on the discharge port becomes large. Therefore, leakage of the brake fluid is easy to occur from the clearance between the outer rotor and the inner rotor. However, the above-described rotary pump can prevent leakage of the brake fluid from the clearance. Thereby, it is possible to provide a braking apparatus capable of excellently carrying out braking operation by using the above-described rotary pump.
Further, according to the braking apparatus, the rotary pump can suck the brake fluid of a first fluid pressure from the side of the brake fluid pressure generating device, pressurize the brake fluid to a second fluid pressure larger than the first fluid pressure and deliver the brake fluid to the side of the braking force generating device. Therefore, it is preferable to provide, in the main conduit, a differential pressure maintaining device for maintaining a differential pressure between the second fluid pressure applied on the side of the braking force generating device and the first fluid pressure on the side of the brake fluid pressure generating device when the brake fluid pressure applied on the braking force generating device is made higher than the first fluid pressure by the rotary pump.
In this way, even in the case where high pressure discharge by the rotary pump is needed, as mentioned above, leakage of the brake fluid from the discharge port to the intake port can be prevented and the discharge efficiency can be promoted in high pressure discharge of the rotary pump.
In a rotary pump according to a third aspect of the present invention, a low pressure side communicating path for communicating an outer periphery of an outer rotor on a side of an intake port with the intake port and a high pressure side communicating path for communicating the outer periphery of the outer rotor on a side of a discharge port with the discharge port are formed in a casing. A first seal device for restraining flow of a fluid at an intermediary between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor is provided therebetween on a side where a first closed gap portion is formed. A second seal device for restraining flow of the fluid at the intermediary between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor is provided therebetween on a side where a second closed gap portion is formed.
A high pressure portion and a low pressure portion are present on the outer periphery of the outer rotor between the high pressure side communicating path and the low pressure side communicating path. Therefore, by installing the first and second seal devices between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor, the high pressure portion can be separated from the low pressure portion. That is, because the first closed gap portion and the second closed gap portion are present between the high pressure side communicating path and the low pressure side communicating path, when the first and the second seal devices are installed respectively in correspondence therewith, leakage of the fluid from the high pressure portion to the low pressure portion on the outer periphery of the outer rotor can be prevented. Thereby, the volumetric efficiency of the rotary pump can be promoted and at the same time, the pump can be driven stably.
Each of the first and second seal devices can be constituted by a first seal member arranged on the side of the casing and a second seal member arranged on the side of the outer rotor. It is preferable to form the first seal member by a material having a hardness softer than that of the second seal member.
When the hardness of the first seal member is made softer than that of the second seal member, fabrication error of the outer rotor can be absorbed by the first seal member while ensuring the sealing performance for the fluid by the second seal member.
When the rotary pump is constituted such that an inner teeth portion of the outer rotor forming the first closed gap portion pushes an outer teeth portion of an inner rotor forming the first closed gap portion in driving the pump, it is preferable to install at least the first seal device for restraining flow of the fluid between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor on the side where the first closed gap portion is formed.
When the rotary pump is constituted such that the inner teeth portion of the outer rotor forming the first closed gap portion pushes the outer teeth portion of the inner rotor forming the first closed portion, the outer rotor pushes the inner rotor. Accordingly, the outer rotor moves in the direction of pushing the inner rotor. As a result, the outer rotor and the casing are brought into contact with each other. Therefore, the sealing performance is achieved at the contact portion of the outer rotor and the casing. Therefore, even when the first sealing device is installed only on the side where the first closed gap portion is formed on the outer periphery of the outer rotor between the high pressure side communicating path and the low pressure side communicating path, leakage of fluid from the high pressure portion to the low pressure portion on the outer periphery of the outer rotor can be prevented and an effect similar to that of the above-described can be achieved.
In the above-described constitution, the second seal device for restraining flow of the fluid between the high pressure side communicating path and the low pressure side communicating path on the outer periphery of the outer rotor may be installed on the side where the second closed gap portion is formed.
When the second seal device is installed on the side where the second closed gap portion is formed on the outer periphery of the outer rotor between the high pressure side communicating path and the low pressure side communicating path, the sealing performance can be ensured further firmly than in the case wherein the sealing performance is ensured by a portion where the outer rotor and the casing are brought into contact with each other. Therefore, leakage of fluid from the high pressure portion to the low pressure portion on the outer periphery of the outer rotor can further effectively be prevented.
Specifically, by arranging the first seal device between the first closed gap portion and the low pressure side communicating path on the outer periphery of the outer rotor, the outer rotor can be moved in the direction of pushing the outer teeth portion of the inner rotor forming the first closed gap portion by the inner teeth portion of the outer rotor forming the first closed gap portion.
Further, when the first seal device is arranged at the above-described position, by installing a third seal device for restraining flow of the fluid between the high pressure side communicating path and the second closed gap portion on the outer periphery of the outer rotor therebetween, the outer rotor can be moved in the above-described direction further effectively.
That is, when the third seal device is installed between the high pressure side communicating path and the second closed gap portion on the outer periphery of the outer rotor, pressure of the outer periphery of the outer rotor on a side where the first closed gap portion is formed becomes higher than pressure thereof on a side where the second closed gap portion is formed. The outer rotor is easy to move by that pressure difference and the inner teeth portion of the outer rotor forming the first closed gap portion can push the outer teeth portion of the inner rotor forming the first closed gap portion further strongly.
Further, each of the first, second and third seal device can be constituted by a first seal member arranged on the side of the casing and a second seal member arranged on the side of the outer rotor. It is preferable that hardness of the first seal member is made softer than that of the second seal member as described above.
It is preferable that recessed portions constituting the communicating paths between each of the intake port and the discharge port and the outer periphery of the outer rotor are formed on a face opposed to the outer peripheral portion of the outer rotor in wall faces of the casing constituting a chamber for containing the inner and outer rotors.
By forming the recessed portions constituting the communicating paths in this way, even when fluid is dragged by the outer periphery of the outer rotor during the rotation of the outer rotor, pressure of the fluid on the outer periphery of the outer rotor can be made uniform. Thereby, a rotary pump having further stable and excellent pump function can be constituted.
Further, when the casing is constituted by a central plate and first and second side plates interposing the center plate, the communicating paths can be formed by chamfering corner portions of a hole of the central plate or by forming a groove portion in the peripheral direction of the hole on a wall face forming the hole of the central plate.
Further, the rotary pump according to the third aspect of the present invention is also applicable to a brake apparatus in a similar manner with the rotary pumps according to the first and the second aspects.